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Conventional ERD/ERS quantification
Event-related desynchronization (ERD) and event-related
synchronization (ERS) is the change of signal's power occuring in a
given band, relative to a reference interval, in this experiment
chosen between 4.5 and 3.5 seconds before the movement onset.
Movement-reactive frequency components were detected by comparing
power spectral densities in the reference interval (-4.5 s to -3.5 s)
and in a 1 s-period around the movement (-0.5 to +0.5 s). Frequency
bands, showing significant differences between the reference interval
and the activity interval, were chosen for ERD/ERS computations. The
EEG was digitally band pass filtered in the selected bands (alpha band
10-12 Hz; beta band 14-18 Hz; gamma band 36-40 Hz) and power values
were computed by squaring the samples and averaging these power
samples across trials. To reduce the number of power values (original
signal was sampled 128Hz), 16 consecutive samples were averaged
producing an 8 Hz sampling rate in the resulting power time
series. Absolute band power was converted to percentage power using
the reference interval as 100%. By convention, an ERD corresponds to
power decrease and an ERS to a power increase
[7]. Results are presented in Figure 3.
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Piotr J. Durka
2001-03-23